This invention relates to a vehicular navigation apparatus which provides guidance along a path by outputting guidance information for travel to a desired destination.
A navigation apparatus for automotive vehicles is adapted to provide course guidance for travel to a desired destination to a driver who is unfamiliar with the local geography. Recent years have seen extensive development of such navigation apparatus.
Conventionally, a vehicular navigation apparatus relies upon so-called "route matching" in which a course is set from a starting point to a desired destination before the vehicle begins travelling, with course guidance being provided to the driver in accordance with the course set. In some of these apparatus, a map is displayed on the screen of a CRT and the course is superimposed on the map if the driver designates a specific course. In a case where the navigation apparatus designates an intersection at which a turn is to be made next in accordance with the preset course, the distance to this intersection is displayed numerically or in the form of a graph. When a turn is to be made at an intersection using such a navigation apparatus, the driver observes the course displayed on the map to decide the next intersection at which the turn is to be made, or the driver looks at the numeric or graph display to ascertain the distance to the intersection where the turn is to be made, thereby determining the proper intersection.
However, as mentioned above, the conventional navigation apparatus is such that a course is set from a starting point to a desired destination before the vehicle begins travelling and course guidance is provided to the driver in accordance with the course set. Consequently, if the driver should happen to mistake an intersection and depart from the set course, travel in accordance with the guidance provided by the navigation apparatus will not be able to continue unless the vehicle is returned to the set course. In addition, a decision as to whether or not a predetermined intersection has been passed as specified by the course guidance is based upon detection of travelled distance or a left or right turn as detected by a distance sensor or steering angle sensor, respectively. In actuality, however, detection of travelled distance and steering angle is susceptible to considerable error, which can cause the navigation apparatus to make errors in judgment.
In an effort to solve these problems, Japanese Patent Application Laid-Open (KOKAI) No. 62-51000 proposes a present position input system, which involves inputting the vehicle's present position on a map and displaying a list of place names. Inputting present position makes it possible to perform route matching in a continuous manner.
However, when teaching the navigation apparatus the present position in the system proposed in Japanese Patent Application Laid-Open (KOKAI) No. 62-51000, it is required that the present position on a road map appearing on a display screen be displayed in enlarged form by pressing, with the tip of one's finger, a touch panel on which the display image is superimposed. This makes the apparatus inconvenient to operate. Another problem is that present position cannot be taught correctly from the relationship between the display and the resolution of the touch panel. If the list of place names is displayed so that present position can be selected from the list, it will be necessary for the driver to turn a large number of pages on the display screen if there are many candidates for selection. Conversely, the system will lack comprehensiveness if too few candidates are made available.
The applicant has filed a patent application (U.S. Ser. No. 260,213, filed Oct. 20, 1988) proposing a novel navigation apparatus which relies upon an explorer system instead of the above-described route matching system. In accordance with this system, the coodinates of a plurality of geographical points (e.g., intersections, characterizing structures, etc.) are set and a desired destination is entered, whereupon a course is sought from each geographical point to the desired destination and outputted as guidance information. Navigation is possible even if distance, steering angle and geomagnetic sensors should happen to fail or even if these sensors are not provided. As a result, if the driver strays from a course or changes the desired destination, the apparatus readily provides the driver with guidance to the destination. However, a system through which desired destination, present position and the like can be inputted in simple fashion is required for this navigation apparatus.